Coat five half pint glass jars with nonstick spray. Set aside. Melt butter and chocolate in pan over medium heat.
Off heat, stir sugar into chocolate mixture, then stir in eggs and vanilla til mixed. Set aside to cool slightly
Whisk together flour, salt, and espresso powder. Stir into chocolate mixture.
Reserve 5 mints for garnish; halve remaining and fold into batter. Divide batter evenly among prepared jars. Transfer jars to a 4 to 6 quart slow cooker. Make sure jars don't touch each other or the sides of slow cooker.
Cover slow cooker and cook brownies til beginning to pull away from sides of jars but still slightly gooey in centers on high setting, 2 1/2 to 3 1/2 hours. Uncover, turn off heat and let brownies sit in slow cooker 1 hour before serving. Serve with vanilla ice cream and reserved mints.